Arsenal’s success at the San Siro in the first leg of their Europa League last-16 tie certainly upset the formbook.

The Gunners had lost their previous four matches in all competitions, 2-1 at home against Swedish outfit FK Ostersunds in the previous round in Europa, 3-0 in both the Carabao Cup final at Wembley and Premier League at the Emirates to Manchester City, followed by a 2-1 reverse at lowly Brighton & Hove Albion in their most recent outing before travelling to Milan.

Manager Arsene Wenger was coming under renewed fire from critics – and making somewhat bizarre comments in post-match press conferences – and his side looked shot of confidence, 13 points adrift of a top-four spot and with hopes of qualifying for the Champions League next season resting on them winning the Europa League, as Manchester United had done last term.

Milan, on the other hand, were unbeaten in 13 matches under Gennaro Gattuso and had not conceded a goal in their last six matches, with a home win looking the most likely outcome for most neutral observers.

Arsenal arrived in Italy without ineligible club record signing Pierre-Emerick Aubameyang, his fellow striker and previous record signing Alexandre Lacazette (injured), as well as first-choice wing backs Nacho Monreal and Hector Bellerin, but with some history on their side having become the first English club to beat Milan on their own turf more than a decade earlier, thanks to goals from Cesc Fabregas and Emmanuel Adebayor in a 2-0 triumph.

And Wenger’s Class of 2018 matched that in the first half of this contest, thanks to Henrikh Mkhitaryan’s first goal in an Arsenal shirt – thanks to a deflection – and Aaron Ramsey’s composed finish after a stunning through ball from Mesut Ozil in stoppage time.

They might even have been 4-0 up at the break, after Danny Welbeck saw a good chance saved and Mkhitaryan clipped the crossbar, but Milan had caused a few nervous moments at the other end, none more so than when David Ospina raced from his line and almost brought down Hakan Calhanoglu for an early penalty.

And the hosts might have halved the deficit after the restart, but Giacomo Bonaventura lifted a good chance over the bar.

After that, Arsenal produced a resilient defensive effort to protect their lead – a phrase not often heard in association with their defending in recent times.

Stand-in full-backs Calum Chambers and Sead Kolasinac, either side of central defensive duo Shkodran Mustafi and Laurent Koscielny, frustrated Milan to the delight of the 2,000 travelling Arsenal fans to leave the north London club favourites to progress to the quarter-finals.

And having snapped a morale-sapping run of defeats in such style, players were quick to show their delight on social media.

The watching Aubameyang was among the first to post a simple #COYG and flexed biceps emoji, while Per Mertesacker praised his team-mates from afar and implored them to ‘finish the job at the Emirates’.

Of those to have played in the match, Chambers simply tweeted a photo of himself with the phrase ‘Bosh!!’ and Mustafi simply tweeted a photo of himself making a tackle, while fellow Germany international Ozil posted his customary #YaGunnersYa, followed by ‘our best away performance for a long time’.

Goalscorer Ramsey used a photo of himself rounding Milan keeper Gianluigi Donnarumma and acknowledged ‘After a disappointing run that was a Great performance from the team’ and Colombian keeper Ospina posted a picture of one of his timely tackles with ‘Solida victoria en Milan!’ as well as ‘What a night in Milan!’.

Young unused substitute Eddie Nketiah got in on the act with ‘great shift from the lads’ and former striker Kevin Campbell was also thrilled to see his old club pull off such a memorable win, posting ‘Get in Arsenal!!! 2-0 come on you Gunners!!!’ and following it up with ‘Can I afford to get greedy and want one more away goal!!?!? Please!’

Some sceptics might feel that Arsenal have missed a chance to put the two-legged tie well and truly to bed at the halfway stage by not adding to their tally in the second half.

They had won 3-0 against Ostersunds in Sweden in the previous round after all, and then fallen 2-0 down in the first half of the return leg at home to set nerves jangling, before Kolasinac netted to end the visitors’ hopes of pulling off an almighty shock.

So although this was a fine win over the once-mighty Milan that should be enjoyed, there are still another 90 minutes to come in London and it would be foolish to think it is job done just yet.